[cabfpub] Questions regarding timestamping certificates

Thu Sep 8 15:14:15 UTC 2016

Well, it depends. There are some software vendors that “request” to have the TSA signed by a known certificate, and as they only trust on root certificate, usually to get your timestamps “recognized” you have to sign the TSA with the CA root cert just in case.

De: public-bounces at cabforum.org [mailto:public-bounces at cabforum.org] En nombre de Dimitris Zacharopoulos
Enviado el: jueves, 8 de septiembre de 2016 16:39
Para: Bruce Morton
CC: public at cabforum.org
Asunto: Re: [cabfpub] Questions regarding timestamping certificates

On 8/9/2016 4:59 μμ, Bruce Morton wrote:

Hi Dimitris,

I don’t think that the spirit of BR 6.1.7 would be for a root CA to issue a certificate for a TSA. Also, the members of the Code Signing Working Group have recommended that there be a separate CA for issuing time-stamping certificates which is defined in Appendix B (4) of the Minimum Requirements for Code Signing certificates.

That was my initial reading too and thank you for confirming. If others think that's not the case, please let us know.

You may want to get feedback directly from the vendor of the client software which will validate the time-stamp signatures.

I don't think that will  be necessary because if the standards require a 2 level certificate chain verification, the client software must support it :)

Best regards,
Dimitris.

Bruce.

From: Dimitris Zacharopoulos [mailto:jimmy at it.auth.gr] 
Sent: Thursday, September 8, 2016 9:03 AM
To: Bruce Morton  <mailto:Bruce.Morton at entrust.com> <Bruce.Morton at entrust.com>; public at cabforum.org
Subject: Re: [cabfpub] Questions regarding timestamping certificates

On 8/9/2016 3:07 μμ, Bruce Morton wrote:

Hi Dimitris,

I think the best document to use for Time-stamping Authority is the Minimum Requirements for Code Signing certificates, see https://casecurity.org/wp-content/uploads/2016/07/Minimum-requirements-for-the-Issuance-and-Management-of-code-signing.pdf.

Thanks, Bruce.

Thank you Bruce, you helped me find answers related to my second question. I am not 100% sure if it answers my first question. The minimum requirements for code signing document, describes a scenario where there are explicit Subordinate CA Certificates for TimeStamping but there is no requirement that forbids end-entity certificates to be issued directly from the Root (at least not one I could spot straight away). 

I guess my 1st question is more focused on what is allowed under the currently approved CA/B Forum Baseline Requirements.

Best regards,
Dimitris.

From: public-bounces at cabforum.org [mailto:public-bounces at cabforum.org] On Behalf Of Dimitris Zacharopoulos
Sent: Thursday, September 8, 2016 4:34 AM
To: public at cabforum.org
Subject: [cabfpub] Questions regarding timestamping certificates

Hello everyone,

We are setting up a new Timestamping Authority and we are looking for specific rules that apply to certificates and subCA Certificates related to timestamping. While reading various standards and the CA/B Forum documents, and after looking at various existing implementations of publicly-trusted CAs, I have some questions and would appreciate any feedback from the forum. Although the BRs apply to SSL certificates, some Root Certificates might be used for both SSL and timestamping services. So the questions that follow, apply to CAs that use the same Root Certificate for both SSL and timestamping purposes. Of course, the EV CodeSigning requirements also define some rules for "EV Timestamp Authorities".

1.	Section 6.1.7 of the Baseline Requirements states that the Root CA Private Keys MUST NOT be used to sign end-entity certificates with some exceptions. This exception list does not specifically mention end-entity certificates with EKU id-kp-timeStamping. Are Root CAs allowed to directly issue end-entity certificates for timestamping authorities (end-entity certificates with EKU only id-kp-timeStamping)?
2.	Section 4.9.7 describes the CRL issuance frequency for Subscriber and Subordinate CA Certificates. If there is a Subordinate CA Certificate constrained with EKU id-kp-timeStamping, is an end-entity certificate (with only id-kp-timeStamping) issued from that subCA considered a "Subscriber" Certificate? Should this subCA issue CRLs every 7 days or every 12 months? My understanding (according to section 1.1 of the BRs) is that the end-entity certificates from that subCA are not required to comply with the CA/B Forum BRs. This should allow the CA to choose the CRL issuance (from that restricted subCA), to exceed the 7-day requirement.

Thank you in advance.

Dimitris Zacharopoulos.

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